Cargo bay with space plane

On the flight line

A nose for space travel

Tough tiles

If the fairing fits

A new era begins

A shroud of darkness becomes the X-37B Orbital Test Vehicle, the unmanned space plane design that twice has ventured into orbit on hush-hush missions for the U.S. Air Force. Oh, the Air Force and X-37B maker Boeing don't mind telling you about the launches and landings and the vehicle's remarkable endurance. Just don't bother asking detailed questions about what they're doing with all that time in orbit.

This photo shows the first X-37B, designated OTV-1, on the runway at Vandenberg Air Force Base in California on December 3, 2010, just after it returned from its debut trip into space, which lasted 224 days.

As it turns out, that was just a warmup act. The second X-37B, OTV-2, touched down on Earth at 5:48 a.m. PT on Saturday, June 16, to end its maiden mission, which began with a liftoff on March 5, 2011 -- meaning it was orbit for 469 days, easily doubling the record of its older sibling.

Editors' note: This slideshow was initially published June 14 at 8:42 a.m. PT. It has been updated with details about the landing of OTV-2.

There's a sort of "X Files" or "Fringe" feel to this photo, as technicians in self-contained protective suits close in on the X-37B for initial checks on that December 2010 night. The space plane bears a striking resemblance to the much larger space shuttles, and for a reason -- they share a common heritage in NASA's work on lifting-body vehicles. In fact, the X-37 initially was a NASA project that ran from 1999 through 2004, though the space agency never got as far as building that orbital vehicle. The Air Force and Boeing picked up where NASA left off to build the X-37B.

While there has been much speculation about what sort of a payload the X-37B might be carrying, on what sort of mission -- spying on China from on high? tinkering with satellites, friendly or otherwise? -- it may well be that these are little more than shakedown cruises. The Air Force does allow that program involves testing of guidance systems, avionics, autonomous flight and landing, and so on, along with the operation of unspecified experiments. Of course, there could be some mind games thrown in for good measure.

There is no cockpit on the X-37B because there are no human occupants. The space plane is built to fly autonomously. When the Air Force decides it's time for the mission to end, a signal will be sent from the ground and the vehicle will commence with autonomous re-entry, descent, and landing.

Like the space shuttles, the X-37B is meant to be reusable, and that's one of the biggest attractions. Presumably much cheaper to operate than the shuttles, a fleet of X-37B space planes could conceivably dash to and from orbit on relatively short notice as the need arises, and also linger on target indefinitely. (Wired's Danger Room blog has a good in-depth look at the development and use of the X-37B here.)

After a long slog in orbit, what space plane wouldn't want to head back indoors for a little servicing?

Now that OTV-2 is back on the ground, Boeing and the Air Force will be getting ready for OTV-1 to make its first return trip to space sometime before the end of 2012. "We look forward to the second launch of OTV-1 later this year and the opportunity to demonstrate that the X-37B is an affordable space vehicle that can be repeatedly reused," Paul Rusnock, Boeing vice president of Government Space Systems, said in a statement Saturday.

Power for the X-37B while it's in orbit comes from the sun. The Air Force says the space plane is equipped with gallium arsenide solar cells and lithium ion batteries. This artist's rendering is from 2003, back when the X-37, as yet unbuilt, was still in NASA's hands (PDF).

This artist's rendering, also from a decade ago, gives a sense of the X-37B's size relative to that of the space shuttle. NASA said at the time that two X-37 vehicles could fit in the cargo bay of a shuttle. (The cargo bay of the X-37B, meanwhile, is roughly the size of a pickup truck bed.)

Here's the tale of the tape for the X-37B: It's 29 feet, 3 inches long, stands 9 feet, 6 inches high, and has a wing span of just under 15 feet. Its weight at launch: 11,000 pounds.

In March 2010, back before it ever flew, the X-37B posed for this picture on a runway in Titusville, Fla. During its debut orbital mission that year, the space plane traveled some 91 million miles, according to the Air Force. It's designed to operate in low Earth orbit, or between 110 and 500 miles above Earth.

A very up-to-date design, the X-37B has no hydraulics on board, according to Boeing. Instead, flight controls and brakes are activated through electromechanical means.

The X-37B features more lightweight composite materials, improved insulation on the leading edge of the wings, and tougher heat-shield tiles that "are significantly more durable than the first generation tiles used by the space shuttle," according to a Boeing Web site description. "All avionics on the X-37B are designed to automate all de-orbit and landing functions."

The X-37B stands in front of part of the fairing that protects it during launch, showing off the silica tiles on its underside. Those TUFI (toughened uni-piece fibrous insulation) tiles are said to be more durable than their counterparts on the space shuttle. On the leading edge of the wings, meanwhile, are TUFROC (toughened uni-piece fibrous refractory oxidation-resistant ceramic ) tiles, which NASA named the government winner of its 2011 Invention of the Year Award.

The OTV-1 version of the X-37B lifts off on its maiden voyage atop an Atlas V rocket, ensconced in its fairing, on April 22, 2010. "History was made in December [2010]," Craig Cooning, head of Boeing's Space and Intelligence Systems, said in a statement marking the launch of OTV-2, "when the X-37B became the United States' first unmanned vehicle to return from space and land on its own."